Photoperiodism

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Photoperiodism
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Definitions

• Photoperiod
• Photoperiodism

http//hoopermuseum.earthsci.carleton.ca/vegetatio
n/photoperiodism.gif
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Flowering Plants

• Several flowering plants use the pigment
  phytocrome to sense seasonal changes in day
  length.
• Phytocrome responds to red and far red light.
• Plants use this as an indication to flower.
• Flowering plants can be classified as long day
  plants, short day plants or day neutral plants.

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Liatrus spp.
Cactus spp.
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Cannnabis
Rosaceae Buds
Poppy
Peyote
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Long Day Plants
Sugar beets
Lettuce
Spinach
http//www.williegreensorganicfarm.com/recipes/ima
ges/spinach.jpg
http//www.biologie.uni-hamburg.de/b-online/schaug
arten/varaltissima/Bvaraltissima1.jpg
http//www.worldcommunitycookbook.org/season/guide
/photos/lettuce.jpg
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Short Day Plants
Sunn Hemp
Tobacco
Chrysanthemum
http//www.tobacco.yaia.com/tobaccoindex.jpg
http//www.hlasek.com/foto/chrysanthemum_coronariu
m_4686.jpg
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Day Neutral Plants
Corn
Cucumber
http//www.oznet.ksu.edu/fieldday/kids/pictures/ki
dsfield600/cg_corn.jpg
http//www.ipm.msu.edu/CAT03_veg/images/5-28Cucumb
er.jpg
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Garner and Allard

• First individuals to discover that plants are
  affected by the amount of light they receive in a
  day.
• Worked with tobacco, soybean, cosmos, ragweed,
  spinach, radish, and lettuce.

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Phytochrome

• Major class of pigments.
• Function in the photoperiodic response of plants.
• Phytochromes exist in two interconvertible forms
• PR because it absorbs red (R 660 nm) light
• PFR because it absorbs far red (FR 730 nm) light
  
• These are the relationships
• Absorption of red light by PR converts it into
  PFR
• Absorption of far red light by PFR converts it
  into PR.
• In the dark, PFR spontaneously converts back to
  PR.
• The amount of PFR is what triggers the response.

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http//www.mcdb.ucla.edu/Research/Tobin/img/poster
.jpg
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References

• http//www.ars.usda.gov/is/timeline/light.htm
• http//www.mobot.org/jwcross/duckweed/phytochrome.
  htm
• http//www.cartage.org.lb/en/themes/Sciences/Botan
  icalSciences/PlantReproduction/FloweringPlant/Phot
  operiodism/Photoperiodism.htm
• http//www.biologyreference.com/Ph-Po/Photoperiodi
  sm.html
• Introductory Plant Physiology by G.R. Noggle and
  G.J. Fritz
• Introducing Biological Rhythms by W.L. Koukkari
  and R.B. Sothern
• http//hoopermuseum.earthsci.carleton.ca/vegetatio
  n/9a_photoperiodism.htm